An entity can only be attached as modified without original state if it declares a version member or does not have an update check policy

Question

I hope you can help me. This is an issue I have been battling with for days now, and I am struggling to resolve it.

I have read up quite a bit on this specific error, and it seems there are a couple ways to resolve it. I have unfortunately not been able to.

My error lies on this line:

sourceContext.ProjectMasters.Attach(project, true);

I get the error: An entity can only be attached as modified without original state if it declares a version member or does not have an update check policy.

I have read and tried (where possible) the following solutions:

Entity attachment issues in LINQ

Update check' issue when updating an entity using DataContext Attach method

System.InvalidOperationException: An entity can only be attached as modified

And more ...

It seems the problem lies in this; that I am not updating an unchanged record. However, as far as I can see and understand, the record IS changed.

I am sure it is something simple I am doing wrong, and perhaps just need a set of new eyes on it.

Please remember; I am a newbie :) Thank you for your patience.

  private class ProjectMastersIdentifier
            {
                public int Id { get; set; }
                public string FinanceProjectNumber { get; set; }
                public string ProcessingSignal { get; set; }
            }

        public static void ProcessInstructions()
        {
            using (var sourceContext = new StagingTableDataContext())
            {
                using (var destinationContext = new DestinationTableDataContext())
                {
                    var allProjectNames = destinationContext.THEOPTIONs.Select(u => u.NAME).Distinct().ToList();

                    var instructionGroups = sourceContext.ProjectMasters.
                        Where(u => u.Processing_Result == Unprocessed).
                        Select(
                        u =>
                            new ProjectMastersIdentifier
                            {
                                Id = u.RowID,
                                FinanceProjectNumber = u.Finance_Project_Number,
                                ProcessingSignal = u.Processing_Signal.Trim()
                            }
                        ).GroupBy(u => u.ProcessingSignal.Trim());

                    foreach (var instructionGroup in instructionGroups.Where(u => u.Key == "I"))
                    {
                        foreach (var instruction in instructionGroup)
                        {
                            if (allProjectNames.Contains(instruction.FinanceProjectNumber))
                            {
                                var project = new ProjectMaster
                                {
                                    RowID = instruction.Id,
                                    Processing_Result = Invalid,
                                    Processing_Result_Text = "Project Already Exists"
                                };
                                sourceContext.ProjectMasters.Attach(project, true);
                            }
                            else
                            {
                                var project = new ProjectMaster
                                {
                                    RowID = instruction.Id,
                                    Processing_Result = Unprocessed,
                                    Processing_Result_Text = "Project Does not Exiist...Moving on."
                                };
                                sourceContext.ProjectMasters.Attach(project, true);
                            }
                        }

                sourceContext.SubmitChanges();
            }
        }
    }

Thank you in advance!